NASA's Aquarius Sees Salty Shifts

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Written by Maria-José Viñas

Media contact:
Alan Buis 818-354-0474
NASA Jet Propulsion Laboratory, Pasadena, Calif.
Alan.buis@jpl.nasa.gov

News feature: 2013-074 Feb. 27, 2013

NASA's Aquarius Sees Salty Shifts

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.php?release=2013-074&cid=release_2013-074

The colorful images chronicle the seasonal stirrings of our salty world: Pulses of freshwater
gush from the Amazon River's mouth; an invisible seam divides the salty Arabian Sea from
the fresher waters of the Bay of Bengal; a large patch of freshwater appears in the eastern
tropical Pacific in the winter. These and other changes in ocean salinity patterns are
revealed by the first full year of surface salinity data captured by NASA's Aquarius
instrument.

"With a bit more than a year of data, we are seeing some surprising patterns, especially in
the tropics," said Aquarius Principal Investigator Gary Lagerloef, of Earth & Space
Research in Seattle. "We see features evolve rapidly over time."

Launched June 10, 2011, aboard the Argentine spacecraft Aquarius/Satélite de
Aplicaciones Científicas (SAC)-D, Aquarius is NASA's first satellite instrument specifically
built to study the salt content of ocean surface waters. Salinity variations, one of the main
drivers of ocean circulation, are closely connected with the cycling of freshwater around
the planet and provide scientists with valuable information on how the changing global
climate is altering global rainfall patterns.

The salinity sensor detects the microwave emissivity of the top approximately 1 inch (1 to 2
centimeters) of ocean water – a physical property that varies depending on temperature
and saltiness. The instrument collects data in 240-mile-wide (386 kilometers) swaths in an
orbit designed to obtain a complete survey of global salinity of ice-free oceans every seven
days.

The Changing Ocean

The animated version of Aquarius' first year of data unveils a world of varying salinity
patterns. The Arabian Sea, nestled up against the dry Middle East, appears much saltier
than the neighboring Bay of Bengal, which gets showered by intense monsoon rains and
receives freshwater discharges from the Ganges and other large rivers. Another mighty
river, the Amazon, releases a large freshwater plume that heads east toward Africa or
bends up north to the Caribbean, depending on the prevailing seasonal currents. Pools of
freshwater carried by ocean currents from the central Pacific Ocean's regions of heavy
rainfall pile up next to Panama's coast, while the Mediterranean Sea sticks out in the
Aquarius maps as a very salty sea.

One of the features that stand out most clearly is a large patch of highly saline water
across the North Atlantic. This area, the saltiest anywhere in the open ocean, is analogous
to deserts on land, where little rainfall and a lot of evaporation occur. A NASA-funded
expedition, the Salinity Processes in the Upper Ocean Regional Study (SPURS), traveled
to the North Atlantic's saltiest spot last fall to analyze the causes behind this high salt
concentration and to validate Aquarius measurements.

"My conclusion after five weeks out at sea and analyzing five weekly maps of salinity from
Aquarius while we were there was that indeed, the patterns of salinity variation seen from
Aquarius and by the ship were similar," said Eric Lindstrom, NASA's physical
oceanography program scientist, NASA Headquarters, Washington, and a participant of
the SPURS research cruise.

Future Goals

"The Aquarius prime mission is scheduled to run for three years but there is no reason to
think that the instrument could not be able to provide valuable data for much longer than
that," said Gene Carl Feldman, Aquarius project manager at NASA's Goddard Space
Flight Center in Greenbelt, Md. "The instrument has been performing flawlessly and our
colleagues in Argentina are doing a fantastic job running the spacecraft, providing us a
nice, stable ride."

In future years, one of the main goals of the Aquarius team is to figure out ways to fine-
tune the readings and retrieve data closer to the coasts and the poles. Land and ice emit
very bright microwave emissions that swamp the signal read by the satellite. At the poles,
there's the added complication that cold polar waters require very large changes in their
salt concentration to modify their microwave signal.

Still, the Aquarius team was surprised by how close to the coast the instrument is already
able to collect salinity measurements.

"The fact that we're getting areas, particularly around islands in the Pacific, that are not
obviously badly contaminated is pretty remarkable. It says that our ability to screen out
land contamination seems to be working quite well," Feldman said.

Another factor that affects salinity readings is intense rainfall. Heavy rain can affect salinity
readings by attenuating the microwave signal Aquarius reads off the ocean surface as it
travels through the soaked atmosphere. Rainfall can also create roughness and shallow
pools of freshwater on the ocean surface. In the future, the Aquarius team wants to use
another instrument aboard Aquarius/SAC-D, the Argentine-built Microwave Radiometer, to
gauge the presence of intense rain simultaneously to salinity readings, so that scientists
can flag data collected during heavy rainfall.

An ultimate goal is combining the Aquarius measurements with those of its European
counterpart, the Soil Moisture and Ocean Salinity satellite (SMOS) to produce more
accurate and finer maps of ocean salinity. In addition, the Aquarius team, in collaboration
with researchers at the U.S. Department of Agriculture, is about to release its first global
soil moisture dataset, which will complement SMOS' soil moisture measurements.

"The first year of the Aquarius mission has mostly been about understanding how the
instruments and algorithms are performing," Feldman said. "Now that we have overcome
the major hurdles, we can really begin to focus on understanding what the data are telling
us about how the ocean works, how it affects weather and climate, and what new insights
we can gain by having these remarkable salinity measurements."

Aquarius was built by NASA's Jet Propulsion Laboratory, Pasadena, Calif.; and NASA
Goddard. JPL managed Aquarius through its commissioning phase and is archiving
mission data. Goddard now manages Aquarius mission operations and processes science
data. Argentina's space agency, Comisión Nacional de Actividades Espaciales (CONAE),
provided the SAC-D spacecraft, optical camera, thermal camera with Canada, microwave
radiometer, sensors from various Argentine institutions and the mission operations center.
France and Italy also contributed instruments. For more information about NASA's
Aquarius mission, visit: www.nasa.gov/aquarius .

For a narrated global tour of Aquarius ocean surface salinity measurements,
see: http://www.youtube.com/watch?v=5xQP_B18vMw . A visualization showing
changes in global ocean surface salinity as measured by Aquarius from Dec. 2011
through Dec. 2012 can be seen at: http://www.youtube.com/watch?v=RJVnZnZUUYc -


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